<style>
    .center
    {
        position: absolute;
        margin: auto;
        top: 0;
        right: 0;
        bottom: 0;
        left: 0;
        width: 100px;
        height: 100px;

        background-color: transparent;
        border-radius: 50%;
        box-shadow: 25px 10px 0 0 blue;
    }

</style>
<div class="center"></div>